Email:[email protected] Msn:[email protected] Attn:jeness tel:13682308162 HWCAT CSC2046 FEATURES ● ● ● ● ● ● ● ● ● ● SAME PINOUT AS ADS7846 2.2V TO 5.25V OPERATION 1.5V TO 5.25V DIGITAL I/O INTERNAL 2.5V REFERENCE DIRECT BATTERY MEASUREMENT (0V to 6V) ON-CHIP TEMPERATURE MEASUREMENT TOUCH-PRESSURE MEASUREMENT QSPITM AND SPITM 3-WIRE INTERFACE AUTO POWER-DOWN AVAILABLE IN TSSOP-16, QFN-16, AND VFBGA-48 PACKAGES APPLICATIONS ● ● ● ● ● ● PERSONAL DIGITAL ASSISTANTS PORTABLE INSTRUMENTS POINT-OF-SALE TERMINALS PAGERS TOUCH SCREEN MONITORS CELLULAR PHONES DESCRIPTION The CSC2046 is a next-generation version to the ADS7846 4-wire touch screen controller which supports a low-voltage I/O interface from 1.5V to 5.25V. The CSC2046 is 100% pin-compatible with the existing ADS7846, and will drop into the same socket. This allows for easy upgrade of current applications to the new version. The CSC2046 also has an on-chip 2.5V reference that can be used for the auxiliary input, battery monitor, and temperature measurement modes. The reference can also be powered down when not used to conserve power. The internal reference operates down to 2.7V supply voltage, while monitoring the battery voltage from 0V to 6V. The low-power consumption of < 0.75mW typ at 2.7V (reference off), high-speed (up to 125kHz sample rate), and on-chip drivers make the CSC2046 an ideal choice for battery-operated systems such as personal digital assistants (PDAs) with resistive touch screens, pagers, cellular phones, and other portable equipment. The CSC2046 is available in TSSOP-16, QFN-16, and VFBGA-48 packages and is specified over the –40°C to +85°C temperature range. WUXI HAIWEI SEMICONDUCTOR CORP 1 HWCAT CSC2046 ABSOLUTE MAXIMUM RATINGS(1) +VCC and IOVDD to GND…………………………………………….. –0.3V to +6V Analog Inputs to GND…………………………………………. –0.3V to +VCC + 0.3V Digital Inputs to GND ……………………………………… –0.3V to IOVDD + 0.3V Power Dissipation ……………………………………………………………..250mW Maximum Junction Temperature……………………………………………... +150°C Operating Temperature Range ……………………………………….–40°C to +85°C Storage Temperature Range………………………………………… –65°C to +150°C Lead Temperature (soldering, 10s) ……………………………………………+300°C NOTE: (1) Stresses above these ratings can cause permanent damage. Exposure to absolute maximum conditions for extended periods may degrade device reliability. WUXI HAIWEI SEMICONDUCTOR CORP 2 HWCAT CSC2046 ELECTROSTATIC DISCHARGE SENSITIVITY This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage. ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more susceptible to damage because very small parametric changes could cause the device not to meet its published specifications. PACKAGE/ORDERING INFORMATION(1) NOMINAL MAXIMUM SPECIFIED INTEGRAL PRODUCT PACKAGE- PACKAGE PULLUP PACKAGE TEMPERATURE LINEARITY LEAD DESIGNATOR RESISTOR TRANSPORT ORDERING NUMBER MARKING MEDIA, QUANTITY RANGE ERROR (LSB) VALUES CSC2046 50kΩ ±2 VFBGA-48 GQC –40°C to +85°C AZ2046 CSC2046IGQCR Tape and Reel, 2500 CSC2046-90 90kΩ ±2 VFBGA-48 GQC –40°C to +85°C AZ2046A CSC2046IGQCR-90 Tape and Reel, 2500 CSC2046 50kΩ ±2 PW –40°C to +85°C CSC2046I CSC2046IPW Rails, 100 " " " " " " " CSC2046IPWR Tape and Reel, 2500 CSC2046 50kΩ ±2 QFN-16 RGV –40°C to +85°C CSC2046 CSC2046IRGVT Tape and Reel, 250 " " " " " " " CSC2046IRGVR Tape and Reel, 2500 TSSOP-16 NOTE: (1) For the most current specifications and package information, see the Package Option Addendum located at the end of this data sheet. WUXI HAIWEI SEMICONDUCTOR CORP 3 HWCAT CSC2046 ELECTRICAL CHARACTERISTICS At TA = –40°C to +85°C, +VCC = +2.7V, VREF = 2.5V internal voltage, fSAMPLE = 125kHz, fCLK = 16 • fSAMPLE = 2MHz, 12-bit mode, digital inputs = GND or IOVDD, and +VCC must be • IOVDD, unless otherwise noted NOTES: (1) LSB means least significant bit. With VREF = +2.5V, one LSB is 610μV. (2) Assured by design, but not tested. Exceeding 50mA source current may result in device degradation. (3) Difference between TEMP0 and TEMP1 measurement, no calibration necessary. (4) Temperature drift is –2.1mV/°C. (5) CSC2046 operates down to 2.2V. (6) IOVDD must be +VCC. (7) Combined supply current from +VCC and IOVDD. Typical values obtained from conversions on AUX input with PD0 = 0. WUXI HAIWEI SEMICONDUCTOR CORP 4 HWCAT CSC2046 PIN CONFIGURATION QFN WUXI HAIWEI SEMICONDUCTOR CORP 5 HWCAT CSC2046 PIN DESCRIPTION TSSOP PIN # VFBGA PIN # QFN PIN # NAME DESCRIPTION 1 2 3 4 5 6 7 8 9 10 11 12 B1 and C1 D1 E1 G2 G3 G4 and G5 G6 E7 D7 C7 B7 A6 5 6 7 8 9 10 11 12 13 14 15 16 +VCC X+ Y+ X– Y– GND VBAT AUX VREF IOVDD 13 A5 1 BUSY 14 A4 2 DIN 15 A3 3 16 A2 4 Power Supply X+ Position Input Y+ Position Input X– Position Input Y– Position Input Ground Battery Monitor Input Auxiliary Input to ADC Voltage Reference Input/Output Digital I/O Power Supply Pen Interrupt Serial Data Output. Data is shifted on the falling edge of DCLK. This output is high impedance when is high. Busy Output. This output is high impedance when is high. Serial Data Input. If is low, data is latched on rising edge of DCLK. Chip Select Input. Controls conversion timing and enables the serial input/output register. high = power-down mode (ADC only). External Clock Input. This clock runs the SAR conversion process and synchronizes serial data I/O. DOUT DCLK WUXI HAIWEI SEMICONDUCTOR CORP 6 HWCAT CSC2046 TYPICAL CHARACTERISTICS At TA = +25°C, +VCC = +2.7V, IOVDD = +1.8V, VREF = External +2.5V, 12-bit mode, PD0 = 0, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. WUXI HAIWEI SEMICONDUCTOR CORP 7 HWCAT CSC2046 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, +VCC = +2.7V, IOVDD = +1.8V, VREF = External +2.5V, 12-bit mode, PD0 = 0, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. WUXI HAIWEI SEMICONDUCTOR CORP 8 HWCAT CSC2046 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, +VCC = +2.7V, IOVDD = +1.8V, VREF = External +2.5V, 12-bit mode, PD0 = 0, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. WUXI HAIWEI SEMICONDUCTOR CORP 9 HWCAT CSC2046 TYPICAL CHARACTERISTICS (Cont.) At TA = +25°C, +VCC = +2.7V, IOVDD = +1.8V, VREF = External +2.5V, 12-bit mode, PD0 = 0, fSAMPLE = 125kHz, and fCLK = 16 • fSAMPLE = 2MHz, unless otherwise noted. THEORY OF OPERATION The CSC2046 is a classic successive approximation register (SAR) analog-to-digital converter (ADC). The architecture is based on capacitive redistribution, which inherently includes a sample-and-hold function. The converter is fabricated on a 0.6μm CMOS process. The basic operation of the CSC2046 is shown in Figure 1. The device features an internal 2.5V reference and uses an external clock. Operation is maintained from a single supply of 2.7V to 5.25V. The internal reference can be overdriven with an external, low-impedance source between 1V and +VCC. The value of the reference voltage directly sets the input range of the converter. The analog input (X-, Y-, and Z-Position coordinates, auxiliary input, battery voltage, and chip temperature) to the converter is provided via a multiplexer. A unique configuration of low on-resistance touch panel driver switches allows an unselected ADC input channel to provide power and the accompanying pin to provide ground for an external device, such as a touch screen. By maintaining a differential input to the converter and a differential reference architecture, it is possible to negate the error from each touch panel driver switch’s on-resistance (if this is a source of error for the particular measurement). WUXI HAIWEI SEMICONDUCTOR CORP 10 HWCAT CSC2046 ANALOG INPUT Figure 2 shows a block diagram of the input multiplexer on the CSC2046, the differential input of the ADC, and the differential reference of the converter. Table I and Table II show the relationship between the A2, A1, A0, and SER/ control bits and the configuration of the CSC2046. The control bits are provided serially via the DIN pin—see the Digital Interface section of this data sheet for more details. When the converter enters the hold mode, the voltage difference between the +IN and –IN inputs (as shown in Figure 2) is captured on the internal capacitor array. The input current into the analog inputs depends on the conversion rate of the device. During the sample period, the source must charge the internal sampling capacitor (typically 25pF). After the capacitor has been fully charged, there is no further input current. The rate of charge transfer from the analog source to the converter is a function of conversion rate. WUXI HAIWEI SEMICONDUCTOR CORP 11 HWCAT TABLE I. Input Configuration (DIN), Single-Ended Reference Mode (SER/ TABLE II. Input Configuration (DIN), Differential Reference Mode (SER/ CSC2046 high). low). WUXI HAIWEI SEMICONDUCTOR CORP 12 HWCAT CSC2046 INTERNAL REFERENCE The CSC2046 has an internal 2.5V voltage reference that can be turned on or off with the control bit, PD1 (see Table V and Figure 3). Typically, the internal reference voltage is only used in the single-ended mode for battery monitoring, temperature measurement, and for using the auxiliary input. Optimal touch screen performance is achieved when using the differential mode. The internal reference voltage of the CSC2046 must be commanded to be off to maintain compatibility with the ADS7843. Therefore, after power-up, a write of PD1 = 0 is required to insure the reference is off (see the Typical Characteristics for power-up time of the reference from power-down). FIGURE 3. Simplified Diagram of the Internal Reference. REFERENCE INPUT The voltage difference between +REF and –REF (see Figure 2) sets the analog input range. The CSC2046 operates with a reference in the range of 1V to +VCC. There are several critical items concerning the reference input and its wide voltage range. As the reference voltage is reduced, the analog voltage weight of each digital output code is also reduced. This is often referred to as the LSB (least significant bit) size and is equal to the reference voltage divided by 4096 in 12-bit mode. Any offset or gain error inherent in the ADC appears to increase, in terms of LSB size, as the reference voltage is reduced. For example, if the offset of a given converter is 2LSBs with a 2.5V reference, it is typically 5LSBs with a 1V reference. In each case, the actual offset of the device is the same, 1.22mV. With a lower reference voltage, more care must be taken to provide a clean layout including adequate bypassing, a clean (low-noise, low-ripple) power supply, a low-noise reference (if an external reference is used), and a low-noise input signal. The voltage into the VREF input directly drives the capacitor digital-to-analog converter (CDAC) portion of the CSC2046. Therefore, the input current is very low (typically < 13μA). There is also a critical item regarding the reference when making measurements while the switch drivers are ON. For this discussion, it is useful to consider the basic operation of the CSC2046, (see Figure 1). This particular application shows the device being used to digitize a resistive touch screen. A measurement of WUXI HAIWEI SEMICONDUCTOR CORP 13 HWCAT CSC2046 the current Y-Position of the pointing device is made by connecting the X+ input to the ADC, turning on the Y+ and Y– drivers, and digitizing the voltage on X+ (Figure 4 shows a block diagram). For this measurement, the resistance in the X+ lead does not affect the conversion (it does affect the settling time, but the resistance is usually small enough that this is not a concern). However, since the resistance between Y+ and Y– is fairly low, the on-resistance of the Y drivers does make a small difference. Under the situation outlined so far, it is not possible to achieve a 0V input or a full-scale input regardless of where the pointing device is on the touch screen because some voltage is lost across the internal switches. In addition, the internal switch resistance is unlikely to track the resistance of the touch screen, providing an additional source of error. FIGURE 4. Simplified Diagram of Single-Ended Reference (SER/ analog input). high, Y switches enabled, X+ is This situation can be remedied as shown in Figure 5. By setting the SER/ bit low, the +REF and –REF inputs are connected directly to Y+ and Y–, respectively, which makes the analog-to-digital conversion ratiometric. The result of the conversion is always a percentage of the external resistance, regardless of how it changes in relation to the on-resistance of the internal switches. Note that there is an important consideration regarding power dissipation when using the ratiometric mode of operation (see the Power Dissipation section for more details). As a final note about the differential reference mode, it must be used with +VCC as the source of the +REF voltage and cannot be used with VREF. It is possible to use a high-precision reference on VREF and single-ended reference mode for measurements which do not need to be ratiometric. In some cases, it is possible to power the converter directly from a precision reference. Most references can provide enough power for the CSC2046, but might not be able to supply enough current for the external load (such as a resistive touch screen). WUXI HAIWEI SEMICONDUCTOR CORP 14 HWCAT FIGURE 5. Simplified Diagram of Differential Reference (SER/ analog input). CSC2046 low, Y switches enabled, X+ is TOUCH SCREEN SETTLING In some applications, external capacitors may be required across the touch screen for filtering noise picked up by the touch screen (e.g., noise generated by the LCD panel or backlight circuitry). These capacitors provide a low-pass filter to reduce the noise, but cause a settling time requirement when the panel is touched that typically shows up as a gain error. There are several methods for minimizing or eliminating this issue. The problem is the input and/or reference has not settled to the final steady-state value prior to the ADC sampling the input(s) and providing the digital output. Additionally, the reference voltage may still be changing during the measurement cycle. Option 1 is to stop or slow down the CSC2046 DCLK for the required touch screen settling time. This allows the input and reference to have stable values for the Acquire period (3 clock cycles of the CSC2046; see Figure 9). This works for both the single-ended and the differential modes. Option 2 is to operate the CSC2046 in the differential mode only for the touch screen measurements and command the CSC2046 to remain on (touch screen drivers ON) and not go into power-down (PD0 = 1). Several conversions are made depending on the settling time required and the CSC2046 data rate. Once the required number of conversions have been made, the processor commands the CSC2046 to go into its power-down state on the last measurement. This process is required for X-Position, Y-Position, and Z-Position measurements. Option 3 is to operate in the 15 Clock-per-Conversion mode, which overlaps the analog-to-digital conversions and maintains the touch screen drivers on until commanded to stop by the processor (see Figure 13). WUXI HAIWEI SEMICONDUCTOR CORP 15 HWCAT CSC2046 TEMPERATURE MEASUREMENT In some applications, such as battery recharging, a measurement of ambient temperature is required. The temperature measurement technique used in the CSC2046 relies on the characteristics of a semiconductor junction operating at a fixed current level. The forward diode voltage (VBE) has a well-defined characteristic versus temperature. The ambient temperature can be predicted in applications by knowing the +25°C value of the VBE voltage and then monitoring the delta of that voltage as the temperature changes. The CSC2046 offers two modes of operation. The first mode requires calibration at a known temperature, but only requires a single reading to predict the ambient temperature. A diode is used (turned on) during this measurement cycle. The voltage across the diode is connected through the MUX for digitizing the forward bias voltage by the ADC with an address of A2 = 0, A1 = 0, and A0 = 0 (see Table I and Figure 6 for details). This voltage is typically 600mV at +25°C with a 20μA current through the diode. The absolute value of this diode voltage can vary a few millivolts. However, the TC of this voltage is very consistent at –2.1mV/°C. During the final test of the end product, the diode voltage would be stored at a known room temperature, in memory, for calibration purposes by the user. The result is an equivalent temperature measurement resolution of 0.3°C/LSB (in 12-bit mode). FIGURE 6. Functional Block Diagram of Temperature Measurement Mode. The second mode does not require a test temperature calibration, but uses a two-measurement method to eliminate the need for absolute temperature calibration and for achieving 2°C accuracy. This mode requires a second conversion with an address of A2 = 1, A1 = 1, and A0 = 1, with a 91 times larger current. The voltage difference between the first and second conversion using 91 times the bias current is represented by kT/q • ln (N), where N is the current ratio = 91, k = Boltzmann’s constant (1.38054 • 10–23 electron volts/ degrees Kelvin), q = the electron charge (1.602189 • 10–19 C), and T = the temperature in degrees Kelvin. This method can provide improved absolute temperature measurement over the first mode at the cost of less resolution (1.6°C/LSB). The equation for solving for °K is: WUXI HAIWEI SEMICONDUCTOR CORP 16 HWCAT CSC2046 °K = q • △V/(k • ln (N)) (1) where, V = V (I91) – V (I1) (in mV) ∴°K = 2.573 °K/mV • △V °C = 2.573 •△V(mV) – 273°K NOTE: The bias current for each diode temperature measurement is only on for 3 clock cycles (during the acquisition mode) and, therefore, does not add any noticeable increase in power, especially if the temperature measurement only occurs occasionally. BATTERY MEASUREMENT An added feature of the CSC2046 is the ability to monitor the battery voltage on the other side of the voltage regulator (DC/DC converter), as shown in Figure 7. The battery voltage can vary from 0V to 6V, while maintaining the voltage to the CSC2046 at 2.7V, 3.3V, etc. The input voltage (VBAT) is divided down by 4 so that a 5.5V battery voltage is represented as 1.375V to the ADC. This simplifies the multiplexer and control logic. In order to minimize the power consumption, the divider is only on during the sampling period when A2 = 0, A1 = 1, and A0 = 0 (see Table I for the relationship between the control bits and configuration of the CSC2046). FIGURE 7. Battery Measurement Functional Block Diagram. WUXI HAIWEI SEMICONDUCTOR CORP 17 HWCAT CSC2046 PRESSURE MEASUREMENT Measuring touch pressure can also be done with the CSC2046. To determine pen or finger touch, the pressure of the touch needs to be determined. Generally, it is not necessary to have very high performance for this test, therefore, the 8-bit resolution mode is recommended (however, calculations will be shown here in the 12-bit resolution mode). There are several different ways of performing this measurement. The CSC2046 supports two methods. The first method requires knowing the X-plate resistance, measurement of the X-Position, and two additional cross panel measurements (Z1 and Z2) of the touch screen, as shown in Figure 8. Using Equation 2 calculates the touch resistance: The second method requires knowing both the X-plate and Y-plate resistance, measurement of X-Position and Y-Position, and Z1. Using Equation 3 also calculates the touch resistance: FIGURE 8. Pressure Measurement Block Diagrams. WUXI HAIWEI SEMICONDUCTOR CORP 18 HWCAT CSC2046 DIGITAL INTERFACE See Figure 9 for the typical operation of the CSC2046 digital interface. This diagram assumes that the source of the digital signals is a microcontroller or digital signal processor with a basic serial interface. Each communication between the processor and the converter, such as SPI, SSI, or Microwire™ synchronous serial interface, consists of eight clock cycles. One complete conversion can be accomplished with three serial communications for a total of 24 clock cycles on the DCLK input. The first eight clock cycles are used to provide the control byte via the DIN pin. When the converter has enough information about the following conversion to set the input multiplexer and reference inputs appropriately, the converter enters the acquisition (sample) mode and, if needed, the touch panel drivers are turned on. After three more clock cycles, the control byte is complete and the converter enters the conversion mode. At this point, the input sample-and-hold goes into the hold mode and the touch panel drivers turn off (in single-ended mode). The next 12 clock cycles accomplish the actual analog-to-digital conversion. If the conversion is ratiometric (SER/ = 0), the drivers are on during the conversion and a 13th clock cycle is needed for the last bit of the conversion result. Three more clock cycles are needed to complete the last byte (DOUT will be low), which are ignored by the converter. Microwire is a registered trademark of National Semiconductor. Control Byte The control byte (on DIN), as shown in Table III, provides the start conversion, addressing, ADC resolution, configuration, and power-down of the CSC2046. Figure 9 and Tables III and IV give detailed information regarding the order and description of these control bits within the control byte. Bit7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 S A2 A1 A0 MODE Bit 2 SER/ Bit 1 Bit 0 (LSB) PD1 PD0 TABLE III. Order of the Control Bits in the Control Byte. WUXI HAIWEI SEMICONDUCTOR CORP 19 HWCAT CSC2046 BIT NAME DESCRIPTION 7 S 6-4 A2-A0 3 MODE 2 SER/ 1-0 PD1-PD0 Start bit. Control byte starts with first high bit on DIN.A new control byte can start every 15th clock cycle in 12-bit conversion mode or every 11th clock cycle in 8-bit conversion mode (see Figure 13). Channel Select bits. Along with the SER/ bit, these bits control the setting of the multiplexer input, touch driver switches, and reference inputs (see Tables I and II). 12-Bit/8-Bit Conversion Select bit. This bit controls the number of bits for the next conversion: 12-bits (low) or 8-bits (high). Single-Ended/Differential Reference Select bit. Along with bits A2-A0, this bit controls the setting of the multiplexer input, touch driver switches, and reference inputs (see Tables I and II). Power-Down Mode Select bits. Refer to Table V for details. TABLE IV. Descriptions of the Control Bits within the Control Byte. Initiate START—The first bit, the S bit, must always be high and initiates the start of the control byte. The CSC2046 ignores inputs on the DIN pin until the start bit is detected. Addressing—The next three bits (A2, A1, and A0) select the active input channel(s) of the input multiplexer (see Tables I, II, and Figure 2), touch screen drivers, and the reference inputs. MODE—The mode bit sets the resolution of the ADC. With this bit low, the next conversion has 12 bits of resolution, whereas with this bit high, the next conversion has 8 bits of resolution. SER/ —The SER/ bit controls the reference mode, either single-ended (high) or differential (low). The differential mode is also referred to as the ratiometric conversion mode and is preferred for X-Position, Y-Position, and Pressure- Touch measurements for optimum performance. The reference is derived from the voltage at the switch drivers, which is almost the same as the voltage to the touch screen. In this case, a reference voltage is not needed as the reference voltage to the ADC is the voltage across the touch screen. In the single-ended mode, the converter reference voltage is always the difference between the VREF and GND pins (see Tables I and II, and Figures 2 through 5 for further information). If X-Position, Y-Position, and Pressure-Touch are measured in the single-ended mode, an external reference voltage is needed. The CSC2046 must also be powered from the external reference. Caution should be observed when using the single-ended mode such that the input voltage to the ADC does not exceed the internal reference voltage, especially if the supply voltage is greater than 2.7V. NOTE: The differential mode can only be used for X-Position, Y-Position, and Pressure-Touch measurements. All other measurements require the single-ended mode. PD0 and PD1—Table V describes the power-down and the internal reference voltage configurations. The internal reference voltage can be turned on or off independently of the ADC. This can allow extra time for the internal reference voltage to settle to the final value prior to making a conversion. Make sure to also WUXI HAIWEI SEMICONDUCTOR CORP 20 HWCAT CSC2046 allow this extra wake-up time if the internal reference is powered down. The ADC requires no wake-up time and can be instantaneously used. Also note that the status of the internal reference power-down is latched into the part (internally) with BUSY going high. In order to turn the reference off, an additional write to the CSC2046 is required after the channel has been converted. FIGURE 9. Conversion Timing, 24 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port. DESCRIPTION PD1 PD0 0 0 Enabled Power-Down Between Conversions. When each conversion is finished, the converter enters a low-power mode. At the start of the next conversion, the device instantly powers up to full power. There is no need for additional delays to ensure full operation, and the very first conversion is valid. The Y– switch is on when in power-down. 0 1 Disabled Reference is off and ADC is on. 1 0 Enabled Reference is on and ADC is off. 1 1 Disabled Device is always powered. Reference is on andADC is ON. TABLE V. Power-Down and Internal Reference Selection. WUXI HAIWEI SEMICONDUCTOR CORP 21 HWCAT CSC2046 OUTPUT The pen-interrupt output function is shown in Figure 10. While in power-down mode with PD0 = 0, the Y– output is connected to the driver is on and connects the Y-plane of the touch screen to GND. The X+ input through two transmission gates. When the screen is touched, the X+ input is pulled to ground through the touch screen. In most of the CSC2046 models, the internal pullup resistor value is nominally 50kΩ, but this may vary between 36K and 67kΩ given process and temperature variations. In order to assure a logic low of 0.35VDD is presented to the be less than 21kΩ. circuitry, the total resistance between the X+ and Y- terminals must The -90 version of the CSC2046 uses a nominal 90kΩ pullup resistor, which allows the total resistance between the X+ and Y- terminals to be as high as 30kΩ. Note that the higher pullup resistance will cause a slower response time of the to a screen touch, so user software should take this into account. The output goes low due to the current path through the touch screen to ground, which initiates an interrupt to the processor. During the measurement cycle for X-, Y-, and Z-Position, the X+ input is disconnected from the internal pull-up resistor. This is done to eliminate any leakage current from the internal pull-up resistor through the touch screen, thus causing no errors. FIGURE 10. Functional Block Diagram. WUXI HAIWEI SEMICONDUCTOR CORP 22 HWCAT CSC2046 Furthermore, the output is disabled and low during the measurement cycle for X-, Y-, and Z-Position. The output is disabled and high during the measurement cycle for battery monitor, auxiliary input, and chip temperature. If the last control byte written to the CSC2046 contains PD0 = 1, the pen-interrupt output function is disabled and is not able to detect when the screen is touched. In order to re-enable the pen-interrupt output function under these circumstances, a control byte needs to be written to the CSC2046 with PD0 = 0. If the last control byte written to the CSC2046 contains PD0 = 0, the pen-interrupt output function is enabled at the end of the conversion. The end of the conversion occurs on the falling edge of DCLK after bit 1 of the converted data is clocked out of the CSC2046. It is recommended that the processor mask the interrupt is associated with whenever the processor sends a control byte to the CSC2046. This prevents false triggering of interrupts when the output is disabled in the cases discussed in this section. FIGURE 11. Conversion Timing, 16 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port. WUXI HAIWEI SEMICONDUCTOR CORP 23 HWCAT CSC2046 16 Clocks-per-Conversion The control bits for conversion n + 1 can be overlapped with conversion n to allow for a conversion every 16 clock cycles, as shown in Figure 11. This figure also shows possible serial communication occurring with other serial peripherals between each byte transfer from the processor to the converter. This is possible, provided that each conversion completes within 1.6ms of starting. Otherwise, the signal that is captured on the input sample-and-hold may droop enough to affect the conversion result. Note that the CSC2046 is fully powered while other serial communications are taking place during a conversion. TABLE VI. Timing Specifications, TA = –40°C to +85°C. FIGURE 12. Detailed Timing Diagram. WUXI HAIWEI SEMICONDUCTOR CORP 24 HWCAT CSC2046 FIGURE 13. Maximum Conversion Rate, 15 Clocks-per-Conversion. Digital Timing Figures 9 and 12 and Table VI provide detailed timing for the digital interface of the CSC2046. 15 Clocks-per-Conversion FIGURE 14. Ideal Input Voltages and Output Codes. WUXI HAIWEI SEMICONDUCTOR CORP 25 HWCAT CSC2046 Figure 13 provides the fastest way to clock the CSC2046. This method does not work with the serial interface of most microcontrollers and digital signal processors, as they are generally not capable of providing 15 clock cycles per serial transfer. However, this method can be used with field programmable gate arrays (FPGAs) or application specific integrated circuits (ASICs). Note that this effectively increases the maximum conversion rate of the converter beyond the values given in the specification tables, which assume 16 clock cycles per conversion. Data Format The CSC2046 output data is in Straight Binary format, as shown in Figure 14. This figure shows the ideal output code for the given input voltage and does not include the effects of offset, gain, or noise. 8-Bit Conversion The CSC2046 provides an 8-bit conversion mode that can be used when faster throughput is needed and the digital result is not as critical. By switching to the 8-bit mode, a conversion is complete four clock cycles earlier. Not only does this shorten each conversion by four bits (25% faster throughput), but each conversion can actually occur at a faster clock rate. This is because the internal settling time of the CSC2046 is not as critical—settling to better than 8 bits is all that is needed. The clock rate can be as much as 50% faster. The faster clock rate and fewer clock cycles combine to provide a 2x increase in conversion rate. POWER DISSIPATION There are two major power modes for the CSC2046: full-power (PD0 = 1) and auto power-down (PD0 = 0). When operating at full speed and 16 clocks-per-conversion (see Figure 11), the CSC2046 spends most of the time acquiring or converting. There is little time for auto power-down, assuming that this mode is active. Therefore, the difference between full-power mode and auto power-down is negligible. If the conversion rate is decreased by slowing the frequency of the DCLK input, the two modes remain approximately equal. However, if the DCLK frequency is kept at the maximum rate during a conversion but conversions are done less often, the difference between the two modes is dramatic. Figure 15 shows the difference between reducing the DCLK frequency (scaling DCLK to match the conversion rate) or maintaining DCLK at the highest frequency and reducing the number of conversions per second. In the latter case, the converter spends an increasing percentage of time in power-down mode (assuming the auto power-down mode is active). Another important consideration for power dissipation is the reference mode of the converter. In the single-ended reference mode, the touch panel drivers are ON only when the analog input voltage is being acquired (see Figure 9 and Table I). The external device (e.g., a resistive touch screen), therefore, is only powered during the acquisition period. In the differential reference mode, the external device must be powered throughout the acquisition and conversion periods (see Figure 9). If the conversion rate is high, this could substantially increase power dissipation. WUXI HAIWEI SEMICONDUCTOR CORP 26 HWCAT CSC2046 FIGURE 15. Supply Current versus Directly Scaling the Frequency of DCLK with Sample Rate or MaintainingDCLK at the Maximum Possible Frequency. also puts the CSC2046 into power-down mode. When goes high, the CSC2046 immediately goes into power-down mode and does not complete the current conversion. The internal reference, however, does not turn off with goes high (PD1 = 0). going high. To turn the reference off, an additional write is required before When the CSC2046 first powers up, the device draws about 20μA of current until a control byte is written to it with PD0 = 0 to put it into power-down mode. This can be avoided if the CSC2046 is powered up with = 0 and DCLK = IOVDD. LAYOUT The following layout suggestions provide the most optimum performance from the CSC2046. Many portable applications, however, have conflicting requirements concerning power, cost, size, and weight. In general, most portable devices have fairly clean power and grounds because most of the internal components are very low power. This situation means less bypassing for the converter power and less concern regarding grounding. Still, each situation is unique and the following suggestions should be reviewed carefully. For optimum performance, care should be taken with the physical layout of the CSC2046 circuitry. The basic SAR architecture is sensitive to glitches or sudden changes on the power supply, reference, ground WUXI HAIWEI SEMICONDUCTOR CORP 27 HWCAT CSC2046 connections, and digital inputs that occur just prior to latching the output of the analog comparator. Therefore, during any single conversion for an n-bitSAR converter, there are n ‘windows’ in which large external transient voltages can easily affect the conversion result. Such glitches can originate from switching power supplies, nearby digital logic, and high-power devices. The degree of error in the digital output depends on the reference voltage, layout, and the exact timing of the external event. The error can change if the external event changes in time with respect to the DCLK input. With this in mind, power to the CSC2046 should be clean and well bypassed. A 0.1μF ceramic bypass capacitor should be placed as close to the device as possible. A 1μF to 10μF capacitor may also be needed if the impedance of the connection between +VCC or IOVDD and the power supplies is high. Low-leakage capacitors should be used to minimize power dissipation through the bypass capacitors when the CSC2046 is in power-down mode. A bypass capacitor is generally not needed on the VREF pin because the internal reference is buffered by an internal op amp. If an external reference voltage originates from an op amp, make sure that it can drive any bypass capacitor that is used without oscillation. The CSC2046 architecture offers no inherent rejection of noise or voltage variation in regards to using an external reference input. This is of particular concern when the reference input is tied to the power supply. Any noise and ripple from the supply appears directly in the digital results. Whereas high-frequency noise can be filtered out, voltage variation due to line frequency (50Hz or 60Hz) can be difficult to remove. The GND pin must be connected to a clean ground point. In many cases, this is the analog ground. Avoid connections which are too near the grounding point of a microcontroller or digital signal processor. If needed, run a ground trace directly from the converter to the power-supply entry or battery-connection point. The ideal layout includes an analog ground plane dedicated to the converter and associated analog circuitry. In the specific case of use with a resistive touch screen, care should be taken with the connection between the converter and the touch screen. Although resistive touch screens have fairly low resistance, the interconnection should be as short and robust as possible. Longer connections are a source of error, much like the on-resistance of the internal switches. Likewise, loose connections can be a source of error when the contact resistance changes with flexing or vibrations. As indicated previously, noise can be a major source of error in touch screen applications (e.g., applications that require a backlit LCD panel). This EMI noise can be coupled through the LCD panel to the touch screen and cause “flickering” of the converted data. Several things can be done to reduce this error, such as using a touch screen with a bottom-side metal layer connected to ground to shunt the majority of noise to ground. Additionally, filtering capacitors from Y+, Y–, X+, and X– pins to ground can also help. Caution should be observed under these circumstances for settling time of the touch screen, especially operating in the single-ended mode and at high data rates. WUXI HAIWEI SEMICONDUCTOR CORP 28 HWCAT CSC2046 PACKAGING INFORMATION Orderable Device Status (1) Package Package Type Drawing Pins Package Eco Plan (2) Lead/Ball Finish MSL Peak Temp (3) Qty CSC2046EIPW PREVIEW TSSOP PW 16 90 None Call TI Call TI CSC2046EIPWR PREVIEW TSSOP PW 16 2000 None Call TI Call TI CSC2046EIZQCR PREVIEW BGA MI ZQC 48 2500 None Call TI SNPB Call TI CROSTA R JUNI OR CSC2046IGQCR ACTIVE VFBGA GQC 48 2500 None CSC2046IPW ACTIVE TSSOP PW 16 100 None CU NIPDAU Level-2-220C-1 YEAR 2500 None CU NIPDAU Level-2-220C-1 YEAR Green CU NIPDAU Level-1-260C-UNLIM CSC2046IPWR ACTIVE TSSOP PW 16 CSC2046IPWRG4 PREVIEW TSSOP PW 16 Level-2A-235C-4 WKS (RoHS & no Sb/Br) CSC2046IRGVR ACTIVE QFN RGV 16 2500 None CU NIPDAU Level-1-235C-UNLIM CSC2046IRGVRG4 ACTIVE QFN RGV 16 2500 Green CU NIPDAU Level-1-260C-UNLIM (RoHS & no Sb/Br) CSC2046IRGVT ACTIVE QFN RGV 16 250 None CU NIPDAU Level-1-235C-UNLIM CSC2046IZQCR ACTIVE BGA MI ZQC 48 2500 Pb-Free SNAGCU Level-3-260C-168 HR CROSTA (RoHS) R JUNI OR CSC2046IZQCR-90 ACTIVE BGA MI ZQC 48 CROSTA 2500 Pb-Free SNAGCU Level-3-260C-168 HR (RoHS) R JUNI OR (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - May not be currently available - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. None: Not yet available Lead (Pb-Free). Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. WUXI HAIWEI SEMICONDUCTOR CORP 29 HWCAT CSC2046 Green (RoHS & no Sb/Br): TI defines "Green" to mean "Pb-Free" and in addition, uses package materials that do not contain halogens, including bromine (Br) or antimony (Sb) above 0.1% of total product weight. (3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDECindustry standard classifications, and peak solder temperature. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. WUXI HAIWEI SEMICONDUCTOR CORP 30 HWCAT CSC2046 WUXI HAIWEI SEMICONDUCTOR CORP 31 HWCAT CSC2046 GQC (S-PBGA-N48) PLASTIC BALL GRID ARRAY NOTES: A. All linear dimensions are in millimeters. B. This drawing is subject to change without notice. C. MicroStar JuniorTM BGA configuration D. Falls within JEDEC MO-225 WUXI HAIWEI SEMICONDUCTOR CORP 32 HWCAT CSC2046 WUXI HAIWEI SEMICONDUCTOR CORP 33 HWCAT PW (R-PDSO-G**) CSC2046 PLASTIC SMALL-OUTLINE PACKAGE 14 PINS SHOWN NOTES: A. All linear dimensions are in millimeters. B. This drawing is subject to change without notice. C. Body dimensions do not include mold flash or protrusion not to exceed 0,15. D. Falls within JEDEC MO-153 WUXI HAIWEI SEMICONDUCTOR CORP 34